The present invention relates generally to methods for treating cupola and electric arc furnace dust and other waste materials generated during manufacturing processes. More specifically, the present invention relates to an environmentally acceptable closed system process for treating environmentally classed heavy metal oxides, generated during ferrous metal and nonferrous scrap remelt operations.
Many industrial plants generate metallic oxide impregnated dust that includes toxic waste in the form of relatively small particulate matter. This dust can include levels of toxic metal oxide particles such as lead, cadmium, and chromium.
For example, many scrap remelt operations utilize electrical arc furnaces to recycle metal products. These furnaces produce a "dust" as a waste by-product. Due to the scrap from which these plants recycle the metals, this dust may include toxic metallic oxides. For example, in recycling engine blocks lead is generated as metallic oxide dust due to the lead that was present in the gasoline that was run through the engine and other waste materials that have become impregnated in the engine block. Likewise, metal scrap that has been painted, when it is recycled may generate lead oxide because the paint is lead based. Chromium is generated from scrap metal when metal that has been coated with zinc chromate is recycled. Likewise, it is also known for cadmium to be generated during the re-melting of scrap metals.
In a typical foundry process, scrap metal is melted in a cupola. One of the by-products produced when scrap metal is melted in a cupola is bag house dust. In a typical foundry process, bag house dust flows out of the top of the cupola, as a dust and gas stream, through a plurality of ducts to a bag house. The bag house usually contains bag filters that are used to filter the gas streams from the furnace.
Typically, the bag house dust contains a variety of types of metallic oxide particles including toxic materials such as lead, chromium, and cadmium in sufficiently high concentrations to be classified as hazardous by the Environmental Protection Agency. Because this dust is generated by subjecting metal particles to high temperatures, the dust contains oxides and is extremely dry.
Typical electric arc furnace bag house dust includes:
______________________________________ Component Weight Percent ______________________________________ Iron 15-18 percent Manganese 2 percent Nickel less than 1 percent Lead 2-6 percent Cadmium 1-2 percent Magnesium 1-4 percent Chromium 1 percent Zinc 35-40 percent Other Balance ______________________________________ (The metallic components are present as oxides.)
Because this dust contains hazardous metallic oxides, it is necessary to treat and dispose of the dust. To this end, prior art foundry processes have, for example, treated the dust by feeding the hazardous dust from the bag house to a feed silo that then mixes the hazardous dust with an additive so that the dust can then be disposed of.
Although the prior art methods can treat the hazardous dust in a manner so that it can be handled in a non-hazardous way, the Environmental Protection Agency considers any process that locates the means for treating the hazardous material outside the manufacturing process unit, i.e. downstream from the bag house, not to be an "enclosed system" which is part of the manufacturing process. See, 40 CFR 260.10. As set forth below, this classification can have important ramifications.
Foundries and other scrap remelt operations are regulated under the authority of the Solid Waste Disposal Act as amended by the Resource Conservation and Recovery Act of 1976 and as amended by the Hazardous and Solid Waste amendments of 1984 (collectively the "RCRA"). The RCRA controls and regulates the collection of bag house dust and like hazardous waste. If a system is not an enclosed system, and generates hazardous dust, then it falls under and requires an RCRA permit prior to construction and operation of the foundry. See, 40 CFR Section 261.4 (c). The process of securing an RCRA permit can take up to one year and incur a cost of up to $100,000.00 to the foundry operator. Therefore, if a means for treating metallic oxide impregnated dust within the manufacturing processing unit were developed it would result in savings in both time and money to the foundry operator.
There is therefore a need for an improved process and apparatus for treating metallic oxide impregnated dust generated during a foundry process.